Allows deferral of a URLRequest just before talking to the network, at

net/http/http_transaction.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_HTTP_HTTP_TRANSACTION_H_
 #define NET_HTTP_HTTP_TRANSACTION_H_
 
 #include "net/base/completion_callback.h"
 #include "net/base/load_states.h"
 #include "net/base/net_export.h"
@@ skipping 10 matching lines @@
 class HttpResponseInfo;
 class IOBuffer;
 struct LoadTimingInfo;
 class X509Certificate;
 
 // Represents a single HTTP transaction (i.e., a single request/response pair).
 // HTTP redirects are not followed and authentication challenges are not
 // answered.  Cookies are assumed to be managed by the caller.
 class NET_EXPORT_PRIVATE HttpTransaction {
  public:
+  // The bool* is used to inform the caller if it needs to defer or not.

[mmenke, 2014/01/07 19:44:05]

I think this could be clearer.

Maybe something like:

// If |*defer| is set to true, the transaction will wait until
// ResumeNetworkStart is called before establishing a connection.
typedef base::Callback<void(bool* defer)> BeforeNetworkStartCallback;

[jkarlin, 2014/01/07 20:10:03]

Done.

+  typedef base::Callback<void(bool*)> BeforeNetworkStartCallback;
+
   // Stops any pending IO and destroys the transaction object.
   virtual ~HttpTransaction() {}
 
   // Starts the HTTP transaction (i.e., sends the HTTP request).
   //
   // Returns OK if the transaction could be started synchronously, which means
   // that the request was served from the cache.  ERR_IO_PENDING is returned to
   // indicate that the CompletionCallback will be notified once response info is
   // available or if an IO error occurs.  Any other return value indicates that
   // the transaction could not be started.
@@ skipping 96 matching lines @@
   virtual bool GetLoadTimingInfo(LoadTimingInfo* load_timing_info) const = 0;
 
   // Called when the priority of the parent job changes.
   virtual void SetPriority(RequestPriority priority) = 0;
 
   // Set the WebSocketHandshakeStreamBase::CreateHelper to be used for the
   // request.  Only relevant to WebSocket transactions. Must be called before
   // Start(). Ownership of |create_helper| remains with the caller.
   virtual void SetWebSocketHandshakeStreamCreateHelper(
       WebSocketHandshakeStreamBase::CreateHelper* create_helper) = 0;
+
+  // Set the callback to receive notification just before network use.
+  virtual void SetBeforeNetworkStartCallback(
+      const BeforeNetworkStartCallback& callback) = 0;
+
+  // Resumes the transaction after being deferred.
+  virtual int ResumeNetworkStart() = 0;
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_TRANSACTION_H_